This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We proposed experiments that test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. Our experiments address the mechanism used by the brain to convert sensory information represented by neurons in the visual cortex to a decision about what this information means for purposes of planning behavior. We showed that neurons in the association cortex of the macaque represent the accumulation of this evidence for one choice and against an alternative. This year, we demonstrated that the mechanism that explains choice and decision time also explains the degree of confidence associated with a choice. We developed a "post-decision wagering" technique to ascertain certainty in the decisions rendered by monkeys (Kiani &Shadlen, 2009). A collaboration with Prof. Wolpert (Cambridge, UK) we confirmed that the mechanism for decision making elucidated in nonhuman primates also explains the behavior of human decision makers. Interestingly, it explains the revision of some decisions after an initial commitment, that is, a form of vacillation or change of mind (Resulaj et al, 2009). Decision-making bridges the gap between sensation and behavior. Nearly all non-reflexive behaviors require the brain to draw upon its sensory cortex to guide future behavior. Thus, the neural mechanisms for the simple decisions we study are likely to lend insight into more complex cognitive strategies. Our experiments ultimately furnish new insights into the causes and treatments of mental disorders affecting perception, planning and reasoning.